Field of the Invention
The invention relates to a device for measuring a filling level of a liquid in a container with an ultrasound sensor, wherein the ultrasound sensor is associated with a damping cup with at least one antechamber, wherein the antechamber comprises at least one outer ring and one inner ring, wherein the inner ring is arranged within the outer ring.
Brief Summary of the Related Art
A generic device for measuring a filling level of a liquid in a container is known from the WO 2008/009277 A1. The container concerned is, in particular, a container for holding engine oil. The oil level in engines is ascertained using ultrasound sensors. These emit sound waves, which reflect at the boundary surface between two media, in this case between gas and oil, and are then received back by the ultrasound sensor. The filling level in the container in which the liquid is present can be ascertained from the recorded travel-time of the sound waves. However, when the engine is running, in particular in a motor vehicle, it is very difficult if not to say impossible to ascertain the filling level of the oil, because the oil is all frothed up with the sound waves reflecting off the gas bubbles in the oil. The values detected are therefore scattered across a wide range. In order to obtain measured values which can be used for evaluation, an unequivocal boundary surface between the media, i.e. gas and oil, is needed. In order to achieve this, the ultrasound sensors are associated with so-called damping cups. Within these damping cups which envelope the measuring section of the ultrasound sensor, the liquid to be measured is calmed and connected with the container only via a small opening in the damping cup which leads into the container. The small opening in the damping cup leading to the container admits fewer gas bubbles into the damping cup. The filling level in the damping cup corresponds to the liquid level outside the damping cup, but it delays fluctuations which are generated for example when the car accelerates or when it drives through bends. In the publications EP 2366984 B1 and WO 2008/009277 A1 the damping cup is associated with pre-volumes or antechambers. These pre-volumes are provided for the purpose of degassing the liquid to be measured such as frothed-up oil, with the effect that the liquid entering the measuring section of the damping cup is relatively free of bubbles. The antechamber has deflecting elements arranged in it, which influence the flow of the liquid in the antechamber. The intention is to achieve a comparatively slow flow with the result that the liquid remains in the antechamber for a comparatively long time giving the gas bubbles time to gas out.